The supply of legally available amphetamines was reduced by about 80% following the 1970 Controlled Substances Act, which classified all amphetamine-type stimulants as Schedule II drugs. This void was filled by the production of "look-alike," drugs designed to mimic the stimulant effect of amphetamines. The main psychoactive agent in many of these preparations is caffeine or caffeine combined with one or more sympathomimetic amines, such as ephedrine and phenylpropanolamine (PPA). Individually, caffeine, ephedrine, and PPA are relatively safe drugs when taken in moderate or therapeutic doses. However, little is known about the behavioral pharmacology of their combined effects in "look-alike" stimulants, including their discriminative stimulus effects or potential for abuse when individuals exceed the therapeutic dosage regimen in an attempt to achieve amphetamine-like euphoria. In a series of studies, we will investigate the subjective, physiological, and discriminative stimulus effects of a stimulant that is widely used on a daily basis (caffeine), some that are used clinically (mazindol, ephedrine, PPA), and some that have known or potential abuse liability (d-amphetamine, mazindol, caffeine/ephedrine/PPA combined "look-alike" stimulants). The knowledge gained from these studies will enable us to draw clearer distinctions among stimulants in terms of their behavioral and subjective effects. Additionally, these studies will provide seminal information concerning the behavioral pharmacology of "look-alike" stimulants, which pose a potential public health risk from a medical and an abuse liability standpoint. Subject testing on the first study began in March, 1992.